The pathological basis of nerve inexcitability in GuillainBarré syndrome has not been established with certainty. We report the clinicopathological findings in a 67-year-old patient with fulminant GuillainBarré syndrome who died 18 days after onset. Three serial electrophysiological studies revealed nerve inexcitability. Antibodies to Campylobacter jejuni were present but there was no antiganglioside reactivity. Spinal root sections revealed extensive and almost pure macrophage-associated demyelination with occasional presence of T lymphocytes and neutrophil leukocytes. Conversely, in femoral, median, and sural nerves the outstanding lesion was axonal degeneration, with some denuded axons remaining. Unmyelinated fibers, posterior root ganglia, and dorsal columns were preserved. Endoneurial postcapillary venules showed plump endothelial cells with loss of their tight junctions. We conclude that both primary demyelination and axonal degeneration secondary to inflammation account for nerve inexcitability. Our findings lend support to the hypothesis of increased endoneurial pressure as the cause of wallerian degeneration in nerve trunks. The Guillain-Barré syndrome (GBS) is an acute or subacute evolving paralytic disease of unestablished etiology with characteristic pathological features of macrophage and lymphocytic infiltration of peripheral nerve with myelin destruction. 2,3 Nerve conduction studies reveal the typical findings of an acute multifocal demyelinating polyradiculoneuropathy consisting of proximal or distal conduction block and slowing of conduction. 1,9,16,39,46,62 In a small proportion of GBS cases, however, one or more peripheral nerves are inexcitable. 1,62,72,73 Because of the scarcity of detailed autopsy studies, 5,[18][19][20]75 the pathological basis of nerve inexcitability in GBS is controversial, three explanations being possible: distal demyelination with conduction block, secondary wallerian degeneration following demyelination, or primary and severe axonopathy. 5,10,[18][19][20]49,72,73,75 Serial electrophysiological studies have shown that conduction block, the physiological hallmark of demyelination, often precedes the appearance of axonal degeneration. 72,73 Exceptionally inexcitable nerves may be an early and inaugural electrophysiologic feature which has been related to axonal degenera-

The myelin protein P 0 has a major structural role in Schwann cell myelin, and the expression of P 0 protein and mRNA in the Schwann cell lineage has been extensively documented. We show here, using in situ hybridization, that the P 0 gene is also activated in a number of other tissues during embryonic development. P 0 mRNA is first detectable in 10-day-old embryos (E10) and is at this time seen only in cells in the cephalic neural crest and in the otic placode/pit. P 0 expression continues in the otic vesicle and at E12 P 0 expression in this structure largely overlaps with expression of another myelin gene, proteolipid protein. In the developing ear at E14, P 0 expression is complementary to expression of serrate and c-ret mRNAs, which later are expressed in sensory areas of the inner ear, while expression of bone morphogenetic protein (BMP)-4 and P 0 , though largely complementary, shows small areas of overlap. P 0 mRNA and protein are detectable in the notochord from E10 to at least E13. In addition to P 0 expression in a subpopulation of trunk crest cells at E11/E12 and in Schwann cell precursors thereafter, P 0 mRNA is also present transiently in a subpopulation of cells migrating in the enteric neural crest pathway, but is down-regulated in these cells at E14 and thereafter. P 0 is also detected in the placode-derived olfactory ensheathing cells from E13 and is maintained in the adult. No signal is seen in cells in the melanocyte migration pathway or in TUJ1 positive neuronal cells in tissue sections. The activation of the P 0 gene in specific tissues outside the nervous system was unexpected. It remains to be determined whether this is functionally significant, or whether it is an evolutionary relic, perhaps reflecting ancestral use of P 0 as an adhesion molecule.

The increased GFAP and vimentin immunoreactivity and the morphometric and cytological changes in rat SON astrocytes may reflect a sustained upregulation of cellular activity with age, resulting in hypertrophy of glial perikarya and cell processes. Several factors that are known to influence the expression of the astrocytic phenotype, such as signals produced by degenerating neurons and activated microglia, as well as variations in neuronal activity are considered possible causes of the age-associated changes in SON astrocytes.

We present a cytological and biochemical study of the cell death of granule cell precursors in developing rat cerebellum following treatment with the cytotoxic agent methylazoxymethanol (MAM) during the first postnatal week. The density of apoptotic figures per square millimeter progressively increases after 6, 12, 24 and 44 h of treatment, whereas cells immunoreactive for proliferating cell nuclear antigen tend to disappear in the external granular layer (EGL). DNA migration on gel electrophoresis reveals a typical ladder pattern of internucleosomal cleavage following MAM treatment, whereas gel electrophoresis of rRNA shows a conspicuous degradation of both 28S and 18S rRNAs. Ultrastructural analysis has revealed the alterations of structures containing chromatin and ribonucleoprotein (RNP) in dying cells of the EGL. The typical granular beaded configuration of the condensed chromatin changes to a denser, more homogeneous texture suggesting nucleosomal disruption. The reorganization of RNP nuclear domains is reflected by the appearance of dispersed nucleoplasmic RNP particles and the formation of a coiled-body-like structure. However, typical nuclear domains involved in the splicing of RNAs, namely interchromatin granule clusters and typical "coiled bodies", are not found in apoptotic cells. Intranuclear bundles of filaments have also been detected. In the cytoplasm, the presence of dispersed single ribosomes is an initial sign of apoptosis. The massive dispersion and disruption of ribosomes detected after 24 h and 44 h of MAM treatment is reflected by the degradation of both 28S and 18s rRNAs. These results show that MAM treatment provides a useful experimental model for the study of apoptosis in the developing central nervous system. The organization of the cell nucleus in cells undergoing apoptosis clearly reflects a disruption of the nuclear compartments involved in transcription and the processing and transport of RNA and is related to the patterns of DNA and rRNA degradation.

The morphology, organization and expression of proliferating cell nuclear antigen (PCNA) and the cytoskeletal proteins vimentin and GFAP in immature Bergmann glial cells were studied after a developmental injury induced by a single dose of the cytotoxic agent methylazoxymethanol (MAM) administered on postnatal day 5. This drug, which produces cell death of cerebellar granule cell precursors, did not induce apoptosis in Bergmann glial cells, which are in a proliferative stage. After MAM treatment, PCNA staining showed a severe depletion of PCNA-positive granule cell precursors, whereas PCNA-positive Bergmann glial nuclei in the Purkinje cell layer were preserved. Moreover, the quantitative analysis revealed an increase in the density of both Purkinje cells and PCNA-positive Bergmann glial cells per mm of Purkinje cell layer in MAM-treated rats relative to age-matched controls, but the numerical ratio between these two cell populations remains invariable after MAM treatment. Vimentin and GFAP immunocytochemistry revealed a reinforcement of the Bergmann glial palisade with overexpression of both proteins and thicker immunoreactive glial processes in MAM-treated rats. At the ultrastructural level, Bergmann glial processes closely associated with dying cells in different stages of apoptosis were observed. Frequently, these processes enclosed dying cells in extracellular compartments. Furthermore, phagosomes containing apoptotic bodies were found in Bergmann fibers of MAM-treated rats. These data indicate that the cell death of granule cell precursors triggers a reactive response in immature Bergmann glia. We suggest that this response reflects the plasticity of Bergmann glia to control the neuronal microenvironment in the maturing molecular layer, protecting healthy cells against the potentially harmful contents of dying cells. In situ labeling of cell death with the TUNEL method revealed that the cell death of granule cell precursors is of the apoptotic type. The participation of ameboid microglial cells in the phagocytosis of apoptotic cells was shown with tomato lectin histochemistry and ultrastructural analysis. Moreover, the presence of mitosis in this microglial population demonstrates its proliferative activity in regions of extensive cell death.